Website Hosting Blog Website Hosting, Web Development, Website Design, Java, Programming & more Skip to content
• Java Tutorial
• Italian Leather Store - Database Project
• Leather Store Sample
• Sample Leather Store Service
• HOME
• Contact
• Blog
• Find Us
DBMS: WAL protocol Leave a reply
WAL protocol Write-ahead logging (WAL) is aUsually both redo and undo information is stored in the log.
Before a block of data in main memory can be output to the database (in nonvolatile storage), all log records pertaining to data in that block must have been output to stable storage. This rule is called the WAL rule. Strictly speaking, the WAL rule requires only that the undo information in the log have been output to stable storage, and permits the redo information to be written later. The difference is relevant in systems where undo information and redo information are stored in separate log records
Write-ahead logging is employed to flush log records to the persistent log file before data pages are written or at commit time
Imagine a program that is in the middle of performing some operation when the machine it is running on loses power. Upon restart, that program might well need to know whether the operation it was performing succeeded, half-succeeded, or failed. If a write-ahead log were used, the program could check this log and compare what it was supposed to be doing when it unexpectedly lost power to what was actually done. On the basis of this comparison, the program could decide to undo what it had started, complete what it had started, or keep things as they are.
This entry was posted in Data Base on November 30, 2012.
Post navigation
- Absence of Boolean Data-Type in DBMS DBMS: Strict 2PL locking protocol ?
Leave a Reply
You must be logged in to post a comment.
Search for:
Recent Posts
• Oracle 11g Joins and Subqueries
• Sample Database Organization exam:
• Inheritance in C++
• C++ Instance and Static Members
• C++ Conditional Statements (if else)
• C++ Expressions and Working with User Data
• Abstract Factory vs. Factory Method Design Pattern
• lateral clauses in SQL
• SQL Versions
• Null Usage in RDBMS
• In RDBMS how does Statistical Data Get Populated?
• RDBMS Architecture | MySQL, MS SQL Server & Oracle
• In-Memory database
• Database Architecture
• Chicago Cars Case Study - Requirements
• Software Engineering vs. Computer Science
• Software Engineering vs. System Engineering
• Multilingual SEO processes (MSEO)
• Final Classes
• Why we cannot declare abstract methods as private or static?
Categories
Recent Comments
• Carol Schmitz on Italian Leather Store - Database Project
• sthiaga1 on SQL Versions
• sthiaga1 on Null Usage in RDBMS
• sthiaga1 on RDBMS Architecture | MySQL, MS SQL Server & Oracle
• sthiaga1 on In-Memory database
Useful Resources
• Java Tutorial
• Italian Leather Store - Database Project
• Leather Store Sample
• Sample Leather Store Service
• HOME
• Contact
• Blog
• Find Us
Pages
• Blog
• Contact
• Find Us
• Home
• Italian Leather Store - Database Project
• Sample Leather Store Service